The present invention relates to the design and manufacture of ultra-small optical probes and methods of using the same. More particularly, the invention relates to the use of such probes in optical beam delivery and optical imaging techniques, such as Optical Coherence Tomography (OCT).
Medical diagnostic techniques which rely on measuring the optical properties of a narrow, twisting lumen (e.g., small arteries and veins) or a small space (e.g., pulmonary airways) require ultra-small optical probes. These probes in turn require ultra-small imaging lenses and associated scanning and beam director elements. There exists a need in the art for ultra-small optical probes capable of being used in diagnostic medical devices such as guidewires, catheters, endoscopes, bronchoscopes, needles, and trocars.
The design of ultra-small optical probes for medical diagnosis has been limited by constraints on lens size. GRaded INdex (GRIN) lenses coupled to a fold mirror have been used in the design of a 1 mm catheter. However, although able to image the aperture of a single-mode fiber onto a vessel wall, the GRIN lens catheter known in the art cannot be scaled smaller than 1 mm since the diameter of the GRIN lens itself is on the order of 1 mm.
Techniques for making very small lenses have been described in the literature. However, these lens have small working distances and although suitable for coupling into laser diodes, do not offer the  greater than 1 mm working distance and the  greater than 1 mm depth-of-field required to image the internal structures of a human body in situ. Microlenses also have been described that can be used for high-power (short focal length) designs. These type of lenses typically use balls or micro-tapers that yield an overall lens diameter bigger than that of a single-mode fiber or have focal lengths that are too short for imaging the internal structures of a body in situ. Microlenses that are designed specifically for highly multimode fibers pose different theoretical considerations than do lenses which may be used with single-mode fibers and those described in the art reduce the size of the original beam rather than increasing it.
The present invention provides an optical fiber-lens system which can deliver light from a single-mode fiber, providing minimum back-reflection and minimum loss of light while delivering a nearly diffraction limited image in the focal plane of a sample. The optical fiber-lens system in combination with beam steering and scanning elements can be used as an optical probe to navigate small, tortuous paths within the human body.
The present invention provides an optical imaging probe comprising a single-mode optical fiber optically coupled to a lens which has substantially the same diameter as the optical fiber. In another embodiment of the invention, the optical imaging probe comprises a coreless fiber optically coupled to the single-mode fiber and the lens. In a further embodiment of the invention, the lens is in communication with a beam director.
The invention also provides an optical probe including a graded index lens. In another embodiment of the invention, the optical probe comprises a fold mirror. In one embodiment of the invention the fold mirror is spaced apart from the lens, while in another embodiment of the invention, the fold mirror is in physical contact with the lens.
The present invention also provides an optical probe having an optical fiber at least partially contained within a probe housing. In another embodiment, the probe housing is in the form of an insertional medical device, such as a guidewire, an endoscope, bronchoscope, a catheter, a needle, and a trocar.
The present invention also provides connectors to connect and disconnect the probe from an optical system. The connectors of the present invention have a first end for coupling to the probe housing of the optical probe and a second end for coupling to the optical system. In another embodiment of the invention, the probe housing is in the form of a guidewire and the first end of the connector has a diameter which is substantially the same size as the diameter of the guidewire.
In one embodiment of the invention, the optical probe comprises a pull back mechanism in communication with one of the housing and the optical fiber. Actuation of the pull back mechanism causes linear motion of at least one of the probe housing and optical fiber relative to the longitudinal axis of the optical fiber.
The present invention also provides an ultra-small lens for use with the optical probes. In one embodiment of the invention, the lens has a working distance of  greater than 1 mm. In a further embodiment of the invention, the depth of field of the lens is  greater than 1 mm. The invention also provides a method of manufacturing an ultra-small lens having these properties. In one embodiment, a graded index fiber is spliced to a coreless fiber. The coreless fiber is then precision cleaved at a predetermined position and spliced to a single-mode fiber. The graded index fiber is then precision cleaved at a proper distance to produce a lens with desired optical properties (e.g., a large working distance and depth of field).
The invention also relates to a method of measuring the optical properties of a test sample in situ. An optical probe is positioned in proximity to the test sample, the optical probe comprising a single-mode optical fiber optically coupled to a lens which is substantially the same diameter as the optical fiber. An optical beam is then transmitted from the optical probe to a sample in situ and light transmitted from the sample is detected.